Regarding radiant heating in house design. In a two or more story house and with radiant tubing in or under the slab on the bottom floor, is it wiser to install tubing under a conventional wood upper floor or would the system provide more comfort, with less effort, if it were in/under a poured (lightweight) upper floor? Of course cost is a consideration but in a central Alaska environment comfort and efficiency weigh in heavily in the final decision.
Thanks
Replies
Whether to go with light wieght slab (high mass) versus staple up or sandwich ( low mass) or not IMO has alot to do with what kind of daily or weekly temperature swings you're subjected to. The slab is going to retain heat longer, but also have much longer heat up and cool down phases.
I would guess in central Alaska you're going to have to design for a pretty constant 100 degree delta ('tween outside and inside).
There's another poster here, Dave Cook, I think, from Alaska, who is very knowledgable on radiant in-floor. He will probably chime in.
David Thomas here, living on Cook Inlet.
Fairbanks sees big swings seasonally (-50F to +90F). And, coming out of a cold snap can be sudden. Down here in Kenai we had a 70F rise in a few days when we and Anchorage went from -35F to +35-40F in 2-3 days around Jan 19th.
As johnny points out, a low mass system (staple up), will respond much better to quick or big temp swings. Not that 1.5" of gypcrete on the second floor is as much mass as 4" of concrete in a slab-on-grade, but I would look to minimize mass where you can. Even consider a richer (more cement) and extra steel in the slab to allow 3" in the field instead of 4". And the more tile, bare concrete or (ugh) vinyl you've got on the big slab, the better. Carpet or real wood floors add insulation on top of the mass and further reduce the responsiveness. Pergo isn't so bad, and they sell a less insulative unlerlayment specifically for RFH.
Strongly consider a outdoor temp sensor that tells the controller to increase water temps in cold weather. And moderate them when it warms up. When it gets really cold, you want a "big hammer" to hit that mass hard and move its temperature up. In mild weather, the same big hammer will knock it to a overshoot (too hot) condition when what you want is a smaller hammer - warm instead of hot water in the slab. David Thomas Overlooking Cook Inlet in Kenai, Alaska
"less insulative unlerlayment "
What is this stuff? I was going to use 3/4" OSB formed into sleepers, with ????on top.
For Pergo and other flavors of the same stuff over RFH, I strongly recommend that you do a "floating floor". The Pergo pieces join to each other but are not fastened down. You leave 1/4" at the edges and cover it with the base molding. Under the Pergo is a 3/16" or so cushy layer to give it a bit of bounce. Much less insulation than my own floor (double 1/2" CDX with 3/4" T&G birch toenailed into the CDX).
With less insulation you get two good things. More BTUs/sq ft for a given RFH water temperature and a more responsive system.David Thomas Overlooking Cook Inlet in Kenai, Alaska
David, do you recall how long it takes to feel the heat through a staple up under plywood/cement backer/ceramic tile using 120 deg water?
I will get it all engineered before doing the house, just wondering if you know what the lag time would be.
Every rfh company at the Vegas show is sending info. REHAU came in today.
PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
Staple-up, no aluminium? About 1.5 hours, I'd say. TO get to 80-90% of quilibrium temperature of the tile. You've got some mass on top and that insulative wood in between.
Staple-up with Al fins? More like 30-40 minutes. The fins get the heat out of the PEX more efficiently.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Thanks David, that makes the outdoor sensor a pretty important anticipator if RFH was the primary heat source.
If I used the slotted plywood with the water line in direct contact with tile thinset, and let incoming shower water of 130-140 run through, I would guess a pretty rapid floor warm up. I have been in some European hotels that produced toasty floors within minutes of turning on the shower. Just kicking the options around. By the way, saw a GFX in Vegas. The copper wound pipe was "squared" and I couldn't seen what bonded it to the copper core pipe. I still think a solder dip would give excellant heat transfer. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
"the outdoor sensor a pretty important anticipator if RFH" Yes. Or include a forced air component, which can be pretty small since the RFH will provide the base load. And the smaller FA responds (by coming on or off) to quicker inputs - solar gain, sun goes behind a cloud, someone leaves a window open, etc.
I'm impressed that the GFX pipe is squared (one side or all 4?) Cu to Cu HX is going to be great. And the interior film is very thin. Good HX would hinge on getting turbulent flow in the wrapped pipe or at least getting it turbulent once every wrap or so (e.g. put a internal bump or pleasure ridges inside the pipe).David Thomas Overlooking Cook Inlet in Kenai, Alaska
Sir David Thomas of the Cook,
Squared all four, as if round pipe passed through a squaring roll former, leaving the corners rounded.
Re: RFH. I will have both forced air,( have to have A/C), and the radiant only in key rooms. Current thinking, the 6 zones are: Master baths (tile floors), foyer(tile), breakfast area (hardwood), office/computer (carpet), great room (hardwood/carpet), sitting area room at end of master bedroom(carpet). Each would have a thermostat for the RFH.
Is there a problem with heating only a portion of a basement floor, poured concrete, and leaving the rest unheated? PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
We had a customer who insisted on doing half the floor.After the pour they changed the layout.The storeroom is now the most comfortable room in the house.
In a hi-mass setup that is well insulated with little air infiltration, lots of separate tstats is excessive. In lo-mass, or changing one of the other variables, it seems like the right idea.
I don't see a problem with leaving part of a slab void of tube. Might consider doubling the tube at the edge, kind of like near an exterior wall.
I agree with cloud on the high mass-watch out for too many thermostats. I have two zones adjoining in a pretty open, yet tiered living area (as opposed to sleeping). I spend a lot of time getting the zone t-stats adjusted so both zones are warm, equal all the time. I was thinking the passive solar aspect would warrant separate controls. That hasn't seemed to be the case. I'll play with the temp setting to get them thinking more as one. Should have just made one zone in the whole downstairs zoned where there was a more defined "room". If you are talking closed in zones, where regulation is wanted or easily putzed with, then maybe you don't listen to me. The high mass areas don't just come up to temp, they take a bit of time. Quicker response areas give you a little more control.
Nothing worse than walking from one zone to another in your bare feet.......especially on ceramic.
How do you have the zones fed? Are you going to put a pump on each zone, or are you using zone valves? Remodeling Contractor just outside the Glass City.
Quittin' Time
People should not be walking constantly barefooted on concrete or tile. Feet were not made for that.
How warm a tile/concrete floor is to bare feet should then not be a consideration.
For walking around barefooted, carpet is best, most forgiving.
Well forgive this ruby, you have a party and all the folks have holes in their mouths and all that red wine and creamy dip stuff falls to your carpet. The next morning the shock of the newly colored sticky shag will quickly outlay the harder surface that you can mop up. Let's not forget dog pee and some of the other catastrophe's that can happen. I'm thinking if you like to stand around, you maybe put slippers on. (G:)Remodeling Contractor just outside the Glass City.
Quittin' Time
>How warm a tile/concrete floor is to bare feet should then not be a consideration.
I hope no one listens to this heretic!!!! Anyone tries to take my heated tile floors out from under my bare feet will be buried under said floor!!!
I am allergic to carpets and have lived in a practically all tile floor for over 32 years and know what I am talking about.
There are heating ducts under the floor and you can tell where they are by the cat.;-)
Those in the bathroom sure feel good to bare feet. The new house will be all tile also and I considered heating elements under some parts of it but then remembered what happens to bare feet if you have to walk around a lot in there.
I wondered about how long those heating elements will last and what it will take to repair them, so went for the simplicity of wearing slippers/house shoes.
I am jealous of your warm floors, but maybe you don't do that much walking on them?
>but then remembered what happens to bare feet if you have to walk around a lot in there.
What happens?
>I am jealous of your warm floors, but maybe you don't do that much walking on them?
All day long, all year long.
First, you are using that heat for more than to warm bare feet. That it does so is a bonus.
A friend built a house about a year ago, all tile but two bedrooms and has been complaining that her feet hurt, can't go barefoot there like she did on her previous wood and carpet house, so I am not the only one that get's sore feet barefooted on tile floors, without more protection.
People working on concrete floors get mats to stand on and good shoes with thick soles for support. People's feet are made to walk on ground that gives a little, conforms to the foot some.
I guess that you are tough!
Was just reading an article saying that some medical center is going to do a study of just how healthful it is to walk on small, egg shaped stones. All sorts of health beneifts are claimed by it and it supposedly is popular in some parts of Asia. So perhaps instead of having a tile floor, you should just have them dump a load of river rock in your living room and you will leaving healthfully ever after...
Calvin, Cloud and Rich, (sounds like a law firm).
Thanks for the input. House in design stage. First floor will be low mass application where I am interested in individual room selection for heat on a room use basis. As an example, if I want to spend a few hours on the computer, I might only turn on RFH in the office, and not try to keep the whole 1st floor warmer than some base temp set for the forced air system.
Kind of like working at desk with feet on a heating pad.
The other concern is the high mass basement where I wondered about differential temp stress on the slab. Since I will try to not have the storage room be "best in show" is there a problem with a large portion of concrete slab being heated, while another portion is storage etc, and not needing heat?
I am open and welcome suggestions regarding individual zone pumps, or manifold pumping with solenoids for zone takeoffs, or any other design.
I think RFH is the most comfortable heat, and I plan to put it where we really live, in a house yet to be built. Your experience is appreciated.
PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
No problem w/o tubes in part of the slab, especially if you have a design reason for it.
I'm glad I left them out of one closet for storage of food stuffs and wines a bit cooler than the house proper. I wish I had left them out of the area with the deep freeze. Warmest spot in the house (between RFH and freezer coils) which makes the freezer work harder.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Thanks, that was the answer I was hoping for, and the reasons for avoiding heat are about the same; paints, food, freezer, cedar closet, fire proof/photo/files room etc. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
"fire proof/photo/files room"
Consider the %RH in that storage room. Of course, during your heating season you probably don't have high humidity anywhere, heated or not. But during your cooling season, you want to keep the clothing and paper in a dehumidified space to avoid mold and mustiness.David Thomas Overlooking Cook Inlet in Kenai, Alaska
You are right, and thanks for reminding me. The one I have now is with all interior walls, three layer sheet rock, galvanized covered door, in basement. It is adjacent to the cedar closet that is also sheet rock under the wood, and both have remained musty free. I will definitely keep it off outside walls. In the tropics (Panama Canal Zone), we had a small light bulb close to the floor to provide just a little heat to keep closet dry, but no A/C. Maybe a very small A/C supply at floor level, like 3" pipe to put a little pos pressure/dry air into room.
Re humidity, have to work hard to keep rel humidity above 30-35% this winter. Big freestanding system in use all winter in upstairs hall.
Paul Energy Consultant and author of Practical Energy Cost Reduction for the Home
Edited 2/9/2004 8:44:59 AM ET by Paul Hayden
Quoting myself from over on the humidity in the cabin question, but maybe also helpful for your fire-safe roomlet:
Another idea for moldy books and musty linens is a trick from sailors. Little containers of a salt with a reservior underneath. Take humidity from the air and leaves salty water in the reservior.
You'd need a ton of them in even a small cabin (versus a boat which is really quite a small volume and perfectly water- / air-tight on 5 sides). But maybe a foot locker or big tupperware container or a dedicated and tightly sealed closet (with an exterior-type, weather-stripped door) with those salt-based dehumidifiers. Available at West Marine or most any chandlery.
http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&productId=11648&catalogId=10001&classNum=380&subdeptNum=379&storeNum=12
and http://www.westmarine.com/webapp/wcs/stores/servlet/ProductDisplay?storeId=10001&langId=-1&catalogId=10001&productId=119932&catalogId=10001&classNum=380&subdeptNum=379&storeNum=12
West Marine also offes little warm rods (like your light-bulb idea). To dry out a closet or other small space.David Thomas Overlooking Cook Inlet in Kenai, Alaska
Thanks, Dave.
Very interesting thread.
DW and I looked at cork flooring yesterday. Loved the look and the "eco" slant. Comes in panels 1/2" thick and 12" X 36" I think, although it is probably metric. Snaps together via T&G on edges and ends...manfgrs recommend "floating" install.
Considering using this over 3/4" OSB sleepers with PEX and AL plates on 12" centers. I've already framed door openings in for 1 1/2" between top of subfloor and top of finish floor. What I and some others call the "sandwich" method. Overall exact design still subject to a room-by-room heat loss calculation, BUT:
Would you think I should plan for an intermediate layer between the plates and the cork, or just float the cork right on top of the sleepers and plates?
How would you recommend fastening the plates to the sleepers?
If you can get the Al plates to be pretty flat on the OSB, then no, I wouldn't add a layer of anything in between the plates and the cork. And I wouldn't worry about fastening them down, certainly that connection is not structural. So a dab of construction adhesive in each corner of the Al plate, or a staple to tack it in place just so they don't get kncked around while the cork is going in.
For a second floor, ideally put a bit of insulation underneath (R-11 FG is plenty). The idea is for that heat to up not down. Because there can be times when the upstairs is calling for heat but the downstairs is warm enough and doesn't need a radiant ceiling just then.
Also, in general keep your 1/2" PEX loops under 150 feet in concrete. Maybe 200 or even 250 in a wood floor (much less of a heat sink therefore it needs less BTU quickly).
David Thomas Overlooking Cook Inlet in Kenai, Alaska
We just put in RFH, basement is in concrete, main floor is in concrete (3") and 2nd storey is under the subfloor.
I have to second Dave's suggestion to put insulation on the ceiling of your first floor to push the heat up. We did it under the bathroom, but not the rest of the upstairs, and I think you can tell the difference. (Vinyl is warmer, -- and don't anyone hassle me about vinyl. I'm too old to walk on ceramic.) However, we also put down hardwood (engineered) in the rest of the upstairs, and vinyl in the bathR, so that could make a difference too.
THe heat is more even in the basement and main, -- the basement has to be the absoute warmest of the whole house. The windows are our real heat loss. We thought we were getting good ones, but they have turned out to be really crappy.
The heat is really even, which sometimes is a pain -- if you like to cool the house off when you sleep, well, I've found I just set the thermostat at about 72º and leave it. Takes too long to warm up and cool off, though I have to admit that we're still getting used to how to use it.
However, the oil delivery guy did say that we're not using as much oil as most people, so that's a relief. And we did put in an oil-fired-DHW heater. So something's working.
My suggestion is that you really make sure your windows are installed properly, no leaks around the edges. I would still put in RFH, but poured concrete for the upstairs, and had better windows.
Last week I spent a few hours troubleshooting (via telephone) a problematic rfh installation.
Every room is fine, except for the master bed and bath. Too cold.
After a thorough Q&A and sending the guy into the basement to be my eyes...the installers used a single 670' loop of half-inch PEX to heat (or to TRY to heat) the master bedroom.
ONE loop.
Plus a Taco too small to push.
Cold feet.
Bad installer.
Bad, bad dog...
Good Thread. I have read everyone's postings and have to jump in with a question or two or three (I am currently installing rfh in my 2000sqft addtion and existing house)....
I have zones for the master BR, 2nd floor BR's, basement and main living area (kit, Rec Rm, foyer, DR). Each zone has a maximum loop of 300'. Depending on the size of the zone I will have between 3 and 6 loops. Also, the loops within each zone are layed out in such a fashion that they cover "defined spaces" of that zone (ie. master bedroom - 2 loops in bedroom/carpet, 1 loop in bath/tile. I am planning on having the ability to adjust either flow or mix ratio on the loops to even out the heat within the zones. Any thoughts on this?
Also, I am tossing around the idea of not insulating the floor of the 2 upstairs BR's and letting the heat "leak" into the insulated garage below. The theory being that the bedrooms are in an attic (w/R-38 insul) with only 2 glazings in the dormers. Good idea or bad?
Lastly, no one ever answered the question; one pump w/zone valves or zone pumps?
300' is quite long in a concrete slab. Split it in two. Okay, but borderline on staple-up. Otherwise the zoning set-up seems reasonable.
Leaking heat to the garage - sure, okay to do that. The garage isn't going to get in an over-heated condition and the upstairs bedrooms will lose only a tiny fraction of their heat input to the garage below.
If you have multiple pumps, a single pump failure doesn't leave you without heat.
If you have one (or two) pumps and a zone valve for each zone, then you immediately solve any back-flow problems. But back-flow can occur when a zone and therefore pump is off but another zone is on. The returned water (which is still pretty hot) goes backwards through the off zones. Unless you add check valves to every loop and even then. . . (spring checks aren't great because you lose at least 1/2 psi if you look forever for 1/2 psi checks, more likely you lose 2 psi to the check valve. Or you use swing check valves with little pressure drop but they don't always seat and therefore the back flow continues. On balance, I changed my mind a few years ago and now favor multiple valves whereas I used to prefer multiple pumps.
Also note that you have a lot more options for smart thermostats if they are 24-volts (go to valves directly or through a relay to the pumps). Versus line-voltage thermostats that tend to be pretty dumb with larger hysterysis (dead-pan). A tight dead band is critical in RFH and a even smarter thermostat that can look at trends and outside temps helps even more.David Thomas Overlooking Cook Inlet in Kenai, Alaska
>A tight dead band is critical in RFH
??? New term to me. What's it mean?
David,
It's posts like that that I love to read.
Nice.
Jim, regarding "dead band", he's refering to the "slack" that some thermostats have. Think of a t-stat set for 70. The temp may have to drop to 68 before it actually sends a "start" signal to crank up the heat. Then, once on, it doesn't sent an "off" signal until the temp hits 73. A dead band of 5 degrees. Kind of the tendency of a t-stat to overshoot/undershoot the set, or desired, temp.
If there were no "dead band", or "hysteresis", and the t-stat was as tight as a drum, (think theoretically here) the furnace would be kicking on and off every 60 seconds as the temp hit 70.01 degrees (heat OFF) then cooled to 69.99 degrees (heat ON). Quick cycling leads to wear and tear on a furnace plus less efficient use of fuel.
Edited 2/10/2004 10:05:39 AM ET by Mongo
Thanks. I know that by another term, but now that dead band is in my head, I can't for the life of me think of the other term. Kinda like the opposite of not being able to get a jingle out of your head.
Mongo explained dead band nicely. It isn't always a bad thing as he mentions about a very tight dead band cycling a furnace very rapidly. The dead band should be related to the quickness of your heating system.
Forced air, with it's quick response, is better with a larger dead band, maybe 2 to 4 degrees F. Both to reduce rapid cycling of the furnace and blower but also because your body takes 15-25 minutes to notice a diviation of 2-3 degrees. It is okay to be at 68F for 10 minutes, but it get to seem really cold after an hour. Similiarly, 73F is fine for 5-10 minutes, but feels stifling after 2 hours.
RFH, especially in a 3-4" slab, gains and loses heat so slowly, you want a tighter dead band. If you get to 71F before turning the pump off, you will overshoot, go to 72 or 73 and stay there a long time. What you want is not only to stop at 70.2F, for instance, but for the thermostat/controller to be smart enough to anticipate where the overshoot will go and turn off at, say, 69.4 and climbing, knowing that it will level out at 70F.
Smarter controllers also will do a duty-cycle. They'll look at how much the heat needs to be on (and also may factor in outside temperature) and run the heat that % of the time. Maybe at 30F, the controller observes that the heater needs to run 40% of the time. And the that heat takes 4 hours to reach a new equilibrium. Then it would run 24 minutes on and 36 minutes off each hour. A reasonably long cycle time but one that is so well averaged by the slab that indoor temps would be within 0.2 F or so.
A really smart controller would remember that about operation at 30F and, when outdoor temps were heading down, increase the duty cycle even before the house starts to cool off. At -10F, the same house/heater would need to run about 80% of the time so the controller can start doing that immediately when the outside temps drop. Rather than wait for the house to cool to 69.5. 69.5 ain't bad, but if indoor temps have fallen that much due to outside temps, and the heat comes on only then, there will be a significant undershoot to 67-68F or so. And after 2 hours that starts to feel pretty cold.David Thomas Overlooking Cook Inlet in Kenai, Alaska
David, As the others have posted, this is excellant info, and well appreciated. Q. Are you using domestic house water in your rfh system, ie., open loop?
I just received the Wirsbo total Technical Design Manual, and all parts list, materials, installation manual, a dozen case studies, and the snow melt package. About 1,000 pages in all. Just looking through, I notice some very expensive controllers, manifolds, and parts, as of March pricing 2004. I am going to have to get well educated on this in order to "keep in simple". Don't know whose system I'll use, but this material is certainly a start on designing a system. There seem to be dozens of ways to build a system. Your input is most welcome. PaulEnergy Consultant and author of Practical Energy Cost Reduction for the Home
My system is open for the following reasons:
All the components are food-grade, potable stuff (copper, PEX, SS, brass). I let the city be my expansion tank, just like a normal HWH. I run everything (space and DHW) off a 42,000 BTU HWH so I don't have really hot water to pass through a HX (okay for RFH, but I have a bit of FA in the HRV and a kickspace heater). It is also much easier to purge air from an open system - just blast city water through until it runs clear. Saves one pump, one or more relays, one HX, one expansion tank, plus the manifold and space for all that stuff.
We (an environmental engineer and internal medicine MD) are not concerned about Legionaire's although some people are. But I haven't meet anyone with as many decades of germane schooling and practice that is.
Yeah, RFH components can start to add up. One of those time versus money things - who builds the manifold? Do you get their expensive, smart controller or snag a process controller with PID algorythims off eBay for $40? Buy their packaged pumps/relays or just go to Home Depot and get some bronze Tacos? Lots of choices.David Thomas Overlooking Cook Inlet in Kenai, Alaska
That said, if your inspector says to keep the heating system closed, well there you are. Showing the diagrams from the RFH company and/or the HWH manufacturer for schematics of such systems can help the inspectors comfort level with it.David Thomas Overlooking Cook Inlet in Kenai, Alaska
"the installers used a single 670' loop of half-inch PEX"
And, undoubtably, they didn't leave a diagram of the path of the PEX so that you could propose a reasonable archelogical expedition to dig in and split that loop into 3 or 4 properly sized ones!
David Thomas Overlooking Cook Inlet in Kenai, Alaska
>David Thomas here, living on Cook Inlet.
I thought your name was Thomas Inlet.